Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.
Department of Biomedical Engineering and Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.
PLoS One. 2018 Mar 5;13(3):e0193904. doi: 10.1371/journal.pone.0193904. eCollection 2018.
In particle radiotherapy, range uncertainty is an important issue that needs to be overcome. Because high-dose conformality can be achieved using a particle beam, a small uncertainty can affect tumor control or cause normal-tissue complications. From this perspective, the treatment planning system (TPS) must be accurate. However, there is a well-known inaccuracy regarding dose computation in heterogeneous media. This means that verifying the uncertainty level is one of the prerequisites for TPS commissioning. We evaluated the range accuracy of the dose computation algorithm implemented in a commercial TPS, and Monte Carlo (MC) simulation against measurement using a CT calibration phantom. A treatment plan was produced for eight different materials plugged into a phantom, and two-dimensional doses were measured using a chamber array. The measurement setup and beam delivery were simulated by MC code. For an infinite solid water phantom, the gamma passing rate between the measurement and TPS was 97.7%, and that between the measurement and MC was 96.5%. However, gamma passing rates between the measurement and TPS were 49.4% for the lung and 67.8% for bone, and between the measurement and MC were 85.6% for the lung and 100.0% for bone tissue. For adipose, breast, brain, liver, and bone mineral, the gamma passing rates computed by TPS were 91.7%, 90.6%, 81.7%, 85.6%, and 85.6%, respectively. The gamma passing rates for MC for adipose, breast, brain, liver, and bone mineral were 100.0%, 97.2%, 95.0%, 98.9%, and 97.8%, respectively. In conclusion, the described procedure successfully evaluated the allowable range uncertainty for TPS commissioning. The TPS dose calculation is inefficient in heterogeneous media with large differences in density, such as lung or bone tissue. Therefore, the limitations of TPS in heterogeneous media should be understood and applied in clinical practice.
在粒子放射治疗中，范围不确定性是一个需要克服的重要问题。由于粒子束可以实现高剂量适形性，因此较小的不确定性会影响肿瘤控制或导致正常组织并发症。从这个角度来看，治疗计划系统（TPS）必须准确。但是，在不均匀介质中剂量计算存在众所周知的不准确性。这意味着验证不确定性水平是 TPS 调试的前提之一。我们评估了商业 TPS 中剂量计算算法的准确性，并通过 CT 校准体模的测量与蒙特卡罗（MC）模拟进行了比较。为插入体模的八种不同材料生成了治疗计划，并使用室阵列测量二维剂量。通过 MC 代码模拟了测量设置和束流输送。对于无限固体水体模，测量值与 TPS 之间的伽马通过率为 97.7％，测量值与 MC 之间的伽马通过率为 96.5％。但是，对于肺组织，测量值与 TPS 之间的伽马通过率为 49.4％，而对于骨组织，测量值与 MC 之间的伽马通过率为 85.6％。对于肺组织和骨组织，测量值与 TPS 之间的伽马通过率分别为 67.8％和 100.0％，而对于脂肪组织、乳房组织、脑组织、肝脏组织和骨矿物质，测量值与 MC 之间的伽马通过率分别为 91.7％、90.6％、81.7％、85.6％和 85.6％。对于脂肪组织、乳房组织、脑组织、肝脏组织和骨矿物质，MC 计算的伽马通过率分别为 100.0％、97.2％、95.0％、98.9％和 97.8％。总之，所描述的过程成功地评估了 TPS 调试的允许范围不确定性。在密度差异较大的不均匀介质（如肺或骨组织）中，TPS 剂量计算效率低下。因此，应理解 TPS 在不均匀介质中的局限性，并将其应用于临床实践。
